/Engine/Source/Runtime/Slate/Public/Widgets/SViewport.h
After OnCursorQuery has specified a cursor type the system asks each widget under the mouse to map that cursor to a widget. This event is bubbled.TOptional<TSharedRef>() if you don't have a mapping otherwise return the Widget to show.
virtual [TOptional](API\Runtime\Core\IO\TOptional)< [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > > OnMapCursor ( const [FCursorReply](API\Runtime\SlateCore\Input\FCursorReply) & CursorReply ) const